Date: Mon, 17 May 2010 19:28:06 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Matthew Fleming <matthew.fleming@isilon.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, Zachary Loafman <zml@freebsd.org>, src-committers@freebsd.org Subject: Re: svn commit: r208003 - in head/sys: kern sys Message-ID: <20100517162806.GM83316@deviant.kiev.zoral.com.ua> In-Reply-To: <06D5F9F6F655AD4C92E28B662F7F853E021D4D66@seaxch09.desktop.isilon.com> References: <201005122124.o4CLOk3b027904@svn.freebsd.org> <20100516050651.GZ83316@deviant.kiev.zoral.com.ua> <06D5F9F6F655AD4C92E28B662F7F853E021D4D66@seaxch09.desktop.isilon.com>
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--n8d7KAgWmJ23Ts4y Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, May 17, 2010 at 08:33:52AM -0700, Matthew Fleming wrote: > > From: Kostik Belousov [mailto:kostikbel@gmail.com] > > On Wed, May 12, 2010 at 09:24:46PM +0000, Zachary Loafman wrote: > > > Author: zml > > > Date: Wed May 12 21:24:46 2010 > > > New Revision: 208003 > > > URL: http://svn.freebsd.org/changeset/base/208003 > > >=20 > > > Log: > > > Add VOP_ADVLOCKPURGE so that the file system is called when purging > > > locks (in the case where the VFS impl isn't using lf_*) > > > =20 > > > Submitted by: Matthew Fleming <matthew.fleming@isilon.com> > > > Reviewed by: zml, dfr > >=20 > > After looking at what happen to nullfs, see r208003, I wonder why > > the vop is needed. It is called after VOP_RECLAIM is called by vgonel(), > > after fs-specific data are destroyed. So, on the one hand, vop can only > > operate on struct vnode proper, on the other hand, the actions performed > > by vop_advlockpurge implementation can be done by vop_reclaim as well. > >=20 > > Could you, please, give some details on the supposed use of the vop ? >=20 > >From a design perspective, it makes little sense to allow overriding > the advlock operation, but not the purge. A specific example is if an > implementation does not use struct lockf to implement advlock, then > the hack you mention of purging in VOP_RECLAIM is needed. > > After looking over the history of the changes, I believe it would be > sufficient to have the lock purge done before the reclaim. The vnode > is locked exclusively for both operations, so I don't believe there > will be any timing windows. But I am still not 100% sure when the file > lock is used versus the interlock for serializing access to various > fields. > > The advlock VOPs are analogous to the regular VOP_LOCK in that we > expect an implementation may override the VOP and also the data > structures used, e.g. to not use the vnode's v_lock field for the > VOP_LOCK. Thus any code which refers to v_lockf should be wrapped in a > VOP to allow correct overriding. Essentially, my argument is that whatever you do in VOP_ADVLOCKPURGE, can be and should be done in VOP_RECLAIM. This would also cover the v_data issue. --n8d7KAgWmJ23Ts4y Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (FreeBSD) iEYEARECAAYFAkvxbpUACgkQC3+MBN1Mb4jcwQCeItE83uff8FnY+WbI7H0xwDC+ QQAAoMFTDaTO9L/6gYGutbLyqpOoIJZd =PJi1 -----END PGP SIGNATURE----- --n8d7KAgWmJ23Ts4y--
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